1. Field of the Invention
This invention relates to a thermal printer which is provided with a platen roller and a thermal head pressed against the platen roller through the medium of a recording paper and is adapted to form an image on the recording paper.
2. Description of the Related Art
A thermal printer is possessed of a thermal head which is pressed against a platen roller through the medium of a recording paper. The thermal printer comes in two types; the one type using a recording medium in the form of an inked ribbon or inked film and forming an image on the recording paper by transferring the ink applied on this ribbon onto the recording paper and the other type using a recording medium in the form of a thermosensitive paper by directly forming an image on a thermosensitive paper without using any inked ribbon.
The thermal printer of this construction is characterized by having a relatively small size and operating at a low cost as compared with other systems for recording an image on a recording paper. The conventional thermal printer, however, is limited in miniaturization because it requires to secure an exchange space for allowing attachment and detachment of an ink ribbon to and from a frame assembly or printer body and an escape space for allowing retraction of the thermal head during the exchange of the ink ribbon. Further, the conventional thermal printer has unsolved problems concerning further reduction in production cost, reduction in weight, improvement in operability, facilitation of maintenance such as of the thermal head, facilitation of exchange of consumable supplies such as a recording paper and an inked ribbon, facilitation of troubleshooting, and so on.
Japanese Patent Laid-Open 61-68,275, for example, discloses a printer which has an inked film, a thermal head, and a switch drive mechanism for driving the thermal head accommodated in a unit case adapted to be attached to and detached from a printer frame. In this printer, the operator's manual operation of the switch drive mechanism causes the unit case to be attached to or detached from the printer frame and, at the same time, causes the thermal head to be pressed against or moved away from a platen roller disposed inside the printer frame. In this printer, however, since the aforementioned switch drive mechanism for causing the thermal head to be pressed against or moved away from the platen roller is disposed inside the unit case, the unit case is voluminous, heavy, expensive, and irksome in the work of attachment and detachment. Further, the exchange of consumable supplies and the work of troubleshooting are not easy. Thus, this printer has problems concerning reduction in size, reduction in cost, reduction in weight, improvement in operability, etc. The idea of inserting or removing the inked ribbon into or from the printer through the upper side of the printer frame or in the direction of the axis of rotation of the platen roller has been materialized for the purpose of precluding the work of retracting the thermal head during the insertion or removal of the inked ribbon and obviating the necessity for allocating an extra escape space to the retraction. This device, however, has a problem of poor operability because the operation for inserting or removing the inked ribbon into or from the printer frame cannot be carried out on the front side of the printer frame.